1. Technical Field
The present disclosure relates to embroidery frames for use with embroidery sewing machines, and more particularly to such an embroidery frame including upper and lower frames between which workpiece cloth is held and a clamp mechanism pressing the upper frame against the lower frame and retaining the upper frame in the pressing state.
2. Description of the Related Art
In conventional sewing machines capable of performing embroidery sewing, workpiece cloth to be embroidered is held in a tightly stretched state by an embroidery frame detachably attached thereto. Conventional embroidery frames include a type in which outer and inner frames are connected together and disconnected from each other by tightening or loosening an adjusting screw. On the other hand, a clamp type cloth holding frame has recently been proposed as disclosed by JP-H08-238391A published in 1996. The clamp type cloth holding frame comprises lower and upper frames holding workpiece cloth therebetween and clamp mechanisms which press the upper frame against the lower frame thereby to hold the workpiece cloth between the frames.
The aforesaid clamp type cloth holding frame comprises a base frame (lower frame), a pressing frame (upper frame) holding workpiece cloth in cooperation with the base frame therebetween, a pair of clamp mechanisms pressing the pressing frame against the base frame thereby to separably fix the pressing frame to the base frame, a connecting mechanism which connects the pressing frame to the base frame so that the pressing frame is swingable up and down, and a pair of air cylinders driving the pressing frame via the connecting mechanism. In this embroidery frame, the air cylinders are actuated so that an input section of the clamp mechanism is lowered. As a result, the pressing frame assumes a pressing position where the pressing frame is pressed against the base frame, and the clamp mechanism assumes a clamping state thereby to reliably hold the workpiece cloth.
In the above-described clamp type cloth holding frame, however, the air cylinders are provided as a drive source for swinging the pressing frame up and down. Thus, the provision of the air cylinders results in a complicated construction, increased size and increased production cost of the clamp mechanism.
In view of the aforesaid problems, a spring member has been proposed to be used in the above-described clamp mechanism to press the upper frame against the lower frame by a spring force thereof, instead of the air cylinders. This construction can simplify the structure of the clamp mechanism and accordingly can decrease the production cost.
However, in the case where the spring force is used to press the upper frame against the lower frame, an amount of flexure is increased when workpiece cloth has a large thickness, whereupon a sufficient spring force can be obtained. On the other hand, the spring force is small when workpiece cloth has a small thickness, whereupon a sufficient holding force cannot be obtained. In particular, when workpiece cloth is made from a slippery material, there is a possibility that the workpiece cloth may be displaced within the embroidery frame and accordingly, cannot be embroidered desirably.